Antimicrobial preservatives are commonly included in aqueous consumer products and industrial products to prolong the useful life of the product during storage and usage. Such consumer products include personal care products, household products, pet-grooming products and like products which are handled by or come in contact with the skin of the user. Industrial products made up as aqueous media can also come in contact with the skin of the user. The presence of water in such aqueous media can support the growth of microorganisms. While some microorganisms can be innocuous, others can be pathogenic to humans.
Microbial growth or contamination also can and frequently does cause deterioration of the product while the is in the trade channels and in the hands of a consumer. This deterioration can undesirably alter a product's attributes rendering it physically or chemically unaesthetic, or shorten the product's useful life making it unmarketable and, in some instances, even be injurious to humans. Thus antimicrobial preservatives are desirable and necessary for inclusion in aqueous consumer products, and cosmetics in particular.
The term "antimicrobial preservative" as used herein refers to a compound or substance that kills microorganisms or prevents, inhibits or retards their growth and reproduction and is included in a product only at a concentration sufficient to prevent spoilage or prevent the growth of inadvertently added microorganisms. Such an antimicrobial preservative extends the useful life of a product but does not contribute to the claimed effects of the product.
The term "personal care products" as used herein, refers to health and cosmetic beauty aid products generally recognized as being formulated for beautifying and grooming the skin and hair. For example, personal care products include cosmetics, toiletries, and over-the-counter pharmaceutical products intended for topical usage.
The term "household products" as used herein refers to products specially formulated for cleaning or caring for hard surfaces, clothing and the like for use in homes or institutions. For example, household products include detergents, cleansers, fabric softeners, room deodorizers, soaps and the like.
The term "industrial products" as used herein refers to products made up in aqueous medium for use in the industrial workplace or for maintaining hard surfaces and which may come in contact with the worker's hands or skin. For example, industrial products can include water-based paints, cutting oils, latex solutions and the like in which microbial growth can arise during storage. Industrial products are frequently supplied in concentrated form and are normally diluted with water by the user. Microbial growth can lead to deterioration of the diluted product, costly interference with mechanical operations and expose the workers to possible skin irritation problems.
Aqueous personal care products, particularly emulsions and solutions having a pH of between about 5 and about 9, can support the growth of some undesirable microorganisms when sufficient water is present, unless an effective preservative is included Even anhydrous personal care products, such as eye shadows, lipsticks and pancake makeups which are repeatedly used, can be subjected to microbial contamination, especially when the product is moistened during use or adsorbs moisture on the exposed surface.
Cosmetic products, in particular, can be subject to microbial contamination during manufacture, packaging, storage, as well as during use. Consequently, there is a growing need for antimicrobial preservative systems having a broad spectrum of antimicrobial activity for use in almost all cosmetics. Desirably, the antimicrobial preservative system should be non-irritating to the skin and effective against those microorganisms of greatest concern over the range of pH values encountered in cosmetic products. Ideally, the antimicrobial preservative system should be cost effective and in a form that can be easily stored, shipped and incorporated into the product during its manufacture.
A number of antimicrobial preservatives suitable for cosmetics are well known from the cosmetic art and literature. A collection of articles discussing the categories of antimicrobial preservatives frequently used in cosmetics, and describing the properties and efficacy of commercially available preservatives can be found in the Preservatives Documentary/Encyclopedia issue of Cosmet. & Toilet., 102, No. 12 (1987), the pertinent disclosures of which are incorporated herein by reference. For convenience, common category names will be used herein where applicable.
In particular, formaldehyde is known to have effective broad spectrum fungicidal and bactericidal activity. However, for cosmetic acceptability, antimicrobial preservation with formaldehyde is preferably provided by binding formaldehyde to a heterocyclic organic compound to be released slowly over time. These type of antimicrobial preservatives are commonly categorized as formaldehyde donors. A particularly effective formaldehyde donor commonly employed in cosmetics is a condensation product of formaldehyde and a hydantoin, namely, a 5,5-dimethylhydantoin-formaldehyde adduct having methylol functional groups bound to one or both of the nitrogen atoms of the hydantoin ring.
In commercial practice, 1,3-dimethylol-5,5dimethylhydantoin, is a popular broad-spectrum antimicrobial agent widely used in numerous cosmetics. This formaldehyde donor is designated the name of "DMDM Hydantoin" in the CTFA Cosmetic Ingredient Dictionary, Third Edition, (hereafter CTFA Dictionary) published in 1982 by The Cosmetic, Toiletry and Fragrance Association, Inc. (Washington, D.C.). For convenience, the CTFA name will be used.
Antimicrobial preservatives in liquid form are particularly desirable for convenient handling during manufacturing processes Until now, however, liquid DMDM Hydantoin was prepared commercially only as an aqueous solution resulting from the reaction of formaldehyde solution, such as formalin, with 5,5-dimethylhydantoin (DMH). Commercially, formalin is supplied as an aqueous solution of 37 percent by weight of formaldehyde usually with up to about 15 percent methanol added to prevent polymerization of the formaldehyde. A description of one commercial procedure can be found in U.S. Pat. No. 3,987,184 the pertinent disclosures of which are incorporated herein by reference.
Liquid aqueous DMDM Hydantoin, though useful, suffers from the following drawbacks. In commerce, solutions containing about 55 weight percent DMDM Hydantoin generally are not cold stable. The term "cold-stable" as used herein denotes a composition that does not tend to crystallize on standing, storage, or during shipping at a temperature of below about -10 degrees C. (below about 14 degrees F.). Moreover, the presence of water in the DMDM Hydantoin solution limits its utility to water-containing media.
There is a need and desire, therefore, for a cold-stable, water-free liquid antimicrobial preservative system comprising a formaldehyde donor, and DMDM Hydantoin in particular. One method aspect of this invention provides such a liquid antimicrobial preservative system prepared in a substantially anhydrous state which can be subsequently incorporated in a medium containing sufficient water to support microbial growth and effectively inhibit or retard such microbial growth.
From experience, the ideal preservation of aqueous personal care products requires a mixture of antimicrobial preservative compounds to effectively achieve broad spectrum activity against microbial growth. Each preservative compound, however, must be separately dissolved in the product during manufacture which adds to the cost and handling steps involved.
For example, other preservatives which are also widely used in commercial cosmetic practice are phenyl esters of parahydroxybenzoic acid and alkyl esters of parahydroxybenzoic acid containing 1 to about 10 carbon atoms in the alkyl group. These compounds are generally called "paraben esters" or "parabens". The term "paraben preservative" as used herein means that at least one paraben ester compound is present. Paraben preservatives have marked bacteriostatic activity against gram positive bacteria and a marked fungistatic activity, but efficacy against pseudomonads is poor. Typically, one or more of the paraben preservatives are also commonly included in products containing formaldehyde-donor preservatives to enhance broad spectrum antimicrobial efficacy.
The parabens, however, are generally supplied as solids which, though water-soluble, require heating to increase their solubility in water. There is a need and desire, therefore, for an antimicrobial preservative system including a formaldehyde donor and at least one paraben preservative, preferably in a clear liquid form, to eliminate the problems associated with dissolving solid preservatives during manufacturing. Another method aspect of this invention provides such a preservative system in substantially anhydrous liquid form.